Coalescence of metals



Patented June 6, 1933 I :"UNITEDYS'TATES HARR 11.; s'ron'r; or annsLnY-on nunson, nnw YORK, assienoa 'ro corrna'nnox- I Parent V amnion CORPORATION, OF NEW YORK, n. Y., A CORPORATION on NEW YORK coALnscnNcn or mats no Drawing.

invention is a process by which an aggrega'te of metallic particles can be coalesced into .a solid homogeneous mass.

The invention relates particularly. to a process in which the surfaces of the metallic ticles to coalesce the particles. After. the.

surfaces ofthe particles have been chemically cleaned suitable steps are taken to protect the particles against the reformation of surface impurities that would interfere with suc- 1 cessful coalescence.

In my Patent No.-1,822,939 for treating metals I hav disclosed a process'in which metallic particles are coalesced after they have been cleaned by a gas. The present process is especially suitedfor coalescing metallic particles which cannot be economicallycleaned by action of a gas, for example,

- particles of metals suchas zinc, tin, aluminum, or of alloys such as brass or bronze. The particles may be in-the form of shotted tin, electrolytically deposited tin, scrap -tin, scrap aluminum, shotted aluminum, scrap zinc,

electroylytically 'deposited zinc, etc. L .It is 9 preferable that each separate particle of, the aggregate be of similar origin and chemical composition in order to produce a product ofuniform chemical composition. v v As a preliminary step all foreign substances 'such as grease, dust, etc., should be removed from the surfaces of 'the particles in any {suitable manner; In cases where the particles are composed of scrap, the surface of which 40 has been coated with another metal not 'de-' sired in the product, for example tinned plate, the. metal coating may be removed b'yany preferred process. The-individual particles of-the aggregate are not limited in size and shape except that.

Process. for

Application filed June 10, 1931. Serial No. 543,894.

the apparatus used forthe process. 5

The term injurious substances will be used hereinv to mean chemical. compounds,-

such as oxides, sulphides, sulphates, --carbonates, etc., which are present on the surfaces of the particles in sufficient amount to interfere with complete coalescence, or if not present in sufficient amount to interfere with present process the metallic particles are treated with a liquid suitable for removing the particular'injurious substance or substances present on the surfaces of the particles. 'For example, for removing .oxides of zinc or. tin from the respective metal sur-' faces, the particles can be treated in a pickling bath of dilute acid. A suitable picklmg bath can be provided to remove any particuthey must be of a size thatcan be handled by lar injurioussub'stance from anyparticular metallicparticles, and the selection of a proper pickling bath for any particular set of conditions is within the knowledge of one skilled theart.

For economy of handling it will in most cases be advisable to press the particles while cold (at room temperature) into bales or briquettes. In the preferred process this briquetting'is-done afterthe particles have been treated in'the pickling bath, but it can be done at any suitable stage of the process. The volume density of the briquettes need no exceed that necessary to give the bri uette suflicient cohesion to "hold together while it is being handled. Ifthe particles are to be coalesced and extruded in the form of tubing, the briquette may be formed with a hole in the center. U a

After the injurious substances have been removed from the surfaces of the particles,

thegchage of particles may ordinarily be transfe ed through the Ordinary room atterior of the furnace, as disclosed in my Patmosphere to the furnace Where the next sp is to be performed, if the transfer is made Without undue delays. But if after cleaningthe particles are stored in ordinary at- 5 mosphere for a long time the surfaces of the particles will again become contaminated with injurious substances and it will be necessary to again clean the surfaces before proceeding with the process.

' In the furnace the particles are heated to the metallic'particles within the range of tem electric furnace now used, in the art for anperatures used for coalescence. For example, in the cases of tin, zinc, aluminum, brass, or bronze, the atmosphere may consist of suit ably dry hydrogen and/or blue water gas and/or any hydrocarbon gas.

A preferred type of heating furnace is the nealing metals, with such minor modifications asare necessary to lnsure being able to maintain the non-ngunous atmosphere on the m ent No. 1,822,939.

The charge is now heated to the coalescing temperature, which may be any temperature in the ran e between the recrystallization point and t e melting point of the metallic particles. -If a temperature in the higher part of this range is used,- a lower coalescing pressure can be used than would be necessary 1 if the temperature were in the lower part of the range. It-is preferable when coalescing an aggregate of-particles whose melt point is above 1100 F. to use a temperature in the lower part of the range on account of the lesser maintenance cost of the 'coalescing apparatus. When coalescing an aggregate of metallic particles whose melting point is be low 1100 F.,it is preferable to use a temperature in the upper part of the range on account of the reduction in the required pressure.

. After the charge of particles has reached the temperature desired, it is transferred to' a coalescing apparatus, The atmosphere in the coalescing apparatus and the atmosphere through which the charge passes from the furnace to the coalescing apparatus must be a non-injurious atmosphere, as previously explained. A preferred type of coalescing apparatus is the extrusion press disclosed in 'my Patent No. 1,822,939.

The charge is now subjected to the pres. sure necessary, at the temperature used, to cause crystal grain growth across all adjacent boundaries of the original metallic particles, thereby coalescing the originally sepa- 1,91aiaa ample, the temperature and pressure now used in the art for extruding 7 0-30 cast brass billets can be conveniently used for coalescing and extruding an aggregate of 70-30 'brassparticles. a g

The co'alesdd mass may be extruded from the coalescing apparatus in any suitable shape, such as rods, bars, angles, hollow billets, tubing,etc.

A subsequent charge inserted in the-press can be coalesced within itself and also to the as I remaining stub of the previously extruded charge, and then the entire coalesced mass consisting of the'stub of the previous charge and the subsequent charge may be extruded in one continuous, homogeneous mass. This process can be carried on indefinitely to produce a single piece of any desired length.

In some cases the economy of the process can be increased by removing injurious substances from the surfaces of the particles and coating them with a minute film of another metal whose presence -inthe coalesced product isnot objectionable. Thus brass or, bronze particles may be washed in a pickling bath of a dilute solution of sulphuric acid and copper sulphate. This bath removes oxides of zinc or copper from the surface of the particles and deposits on the particles an extremely thin film of copper whose presence in the coalesced product is in 'no way objectionable. Particles of tin,. zinc, aluminum, steel or iron can be similarlycoated with a minute film of copper. Thereafter the coated particles are heated in a non-injurious-atmosphere and coalesced as previously explained; The greater economy obtained by copper coating is due to the, fact. that a cheaper non-injurious atmosphere can be used.

Thus, if brass particles are coated with copper the non-injurious atmosphere can be composed largely of steam with only a relatively small percentage of hydrogen or hydrocarbon gas. This steam-hydrogen atmosphere is non-explosive and perfectly harmless, and is more economical than the atmorphere that would have to be used if the brass surfaces were exposed after cleaning.

The physical characteristics of. coalesced and extrudedmetals or alloys is at least as good as the physical characteristic of metals or alloys of the same compositionmade by prior art methods of melting andcasting, when both are subjected to the saine heat treatment and working treatment. I For exiftallic mass from an aggregate of smaller meampleif one inch diameter annealed brass rods are broken up, coalesced. and extruded as one inch diameter brass rods, the extruded rod after annealing. will have the same hysical characteristics (as the one, inch parent brass rods. a

The physical characteristics of the product V I obtained by coalescing and extrudingany aggregate of metallic particles is generally su perior to the product obtained by melting and castin these same particles due to the fact that t e particles while in molten condition are effected by contact with the fur nace walls and furnace slag. v

A product coalesced and extruded from an aggregate of electrolytically deposited metallic particles is the'purest form in which the metal can be produced due to the fact that it is not contaminated by contact with furnace walls and furnace slag which occurs when prior art methods of melting and casting it are used.

The grain structure of a coalesced and extruded product, when viewed with a microscope is the same as is seen in prior-art produced and worked metal of the same composition. All the boundaries of the original metallic particles are obliterated and the entire coalesced and extruded mass possesses which Similarly when a successive charge is inserted and coalesced against the remaining stub, of the previous charge the contact face "between the stub and the successive charge is entirely obliterated and under the microscope shows the same interlocking crystal formation as all other parts of theextruded product. I u

Theadvantagesof coalescence and extru-'.

A sion compared to prior art meltingand castwill vary for each metal or metal alloy; 4 For example if 70-30 scrap brass rods are to be reworked into'brass rods; the following table shows the steps required by each method:

' My process P1101 Pickling I Cabbagin Brlquettlng Melting g Heating I Casting Ooalesclng and extrusion I Cropping Heating Extrusion 'Themelting, casting and cropping which are the most expensive steps'in prior art are dispensed with andthe inexpensive step of scrap-to beagain remelted Whereas in my process I obtain 100% of the original scrap rodsasacceptable product.

I claim 1. The'method'of producing a solid-metallic particles, which consists in treating the -metallic particles in a pickling and .coatmg coalesce all the individual particles into a cohesive mass shaving crystal grain growth across all adjacent'boundaries of the original metallic particles.

2. The method of producing a solid metallic mass from an aggregate of smaller me tallic particles, which consists in treating the metallic particles in a pickling and coat- "ing bath to remove injurious substances and cover the metallic particles with a coating of a ocoalescable metal different from the average metal composition of the particles, said coating metalbeing one which can be treated with a cheaper non-injurious atmosphere than can the uncoated metallic particles, transferring the coated particles to a furnace, thereafter and until the end of the process maintaining the particles in an atmosphere non-injurious to the coating metal, heating the particles to a temperature between the recrystallization point and the melting point of the particles, and subjecting them to pressure suflicient to coalesce all the individual particles into a cohesive mass having crystal grain growth across all adjacent boundaries of the original metallicparticles.

3. The method of producing a solid metaillic mass from an' aggregatejof smaller particles which contain a metal other than copper, which consists in. treating the metallic particles in a pickling and coating bath to remove injurious substances and cover the metallic particles with a coating of copper, transferring the particles to a furnace; thereafter-and until the end of theprocess maintaining the particles in an atmosphere noninjurious to copper, heating the particles to a w temperature between the recrystallization point and the melting point of the particles,

. and subjecting them to pressure 'sufiicient to coalesce all the individual particles into a cohesive-mass having crystal gra n growth across all adjacent boundaries of the original metallic particles.

4.;The-method of producing a solid. metallicmass from an aggregate of smaller particles which contain a-metal other than cop per, which consists in treating the metallic particles in a dilute solution of sulphuric acid and copper sulphate to remove injurious substances and cover the metallic particles with acent boundaries of the original metallic particles.

V V l'l STOUT.

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